Electric vehicles and internal combustion engine powered vehicles may be powered by a number of different fuels. Internal combustion engine powered vehicles may be powered by various fuels including gasoline, diesel, ethanol, methane, or hydrogen, for example. Fuel cells have been proposed as a power source for electric vehicles, and other applications. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode. A common technique for storing large quantities of hydrogen is to cool and compress hydrogen via liquefaction techniques, and to store the liquid phase hydrogen in a cryogenic storage tank. Hydrogen gas liquefies at −253° C. and can be stored at about 70 g/L in the liquid phase. The amount of energy required to compress hydrogen gas into a liquid is very high, and currently may use as much as 40% of the energy obtained from the hydrogen fuel. Thus, it is advantageous to keep the liquid phase hydrogen insulated to militate against liquid evaporation.
Any transfer of heat to the innermost portion of the cryogenic storage tank affects the natural evaporation rate of the cryogenic vessel. The more heat that is transferred, the faster the rate of boil-off of the liquid hydrogen, or the higher the natural evaporation rate. In order to maintain the hydrogen in a liquid state, heat transfer from the ambient environment to the cryogenic liquid must be kept to a minimum. Cryogenic storage tanks generally consist of an inner storage vessel encapsulated with an outer vessel or shell. The space between the inner vessel and the outer vessel is commonly well insulated and under a vacuum. The interior of the tank, however, must include fluid communication, typically in the form of inlet and outlet conduits, for the filling and extraction of liquid and gaseous hydrogen.
A typical storage tank includes a liquid inlet conduit, a liquid outlet conduit, and a gas conduit adapted to be both an inlet and outlet. The three conduits typically penetrate a sidewall of the storage tank through three separate apertures, or together in a common vacuum tube penetrating the sidewall. At least a portion of each conduit is exposed to the ambient environment. The conduits bridge any insulation that is present between the inner and outer vessel and allow heat from the ambient environment to transfer into the inner vessel. Accordingly, there is a need for an improved cryogenic liquid storage tank, and particularly, one that minimizes heat transfer originating from the inlet and outlet conduit.
It would be desirable to develop a cryogenic storage tank with a minimized heat transfer originating from inlet and outlet conduits.